Search Results (1,080)

Dielectric permittivity describes how a material becomes polarized in response to a time-varying electric field and provides a powerful framework for probing the physical organization of biological systems. This review aims to clarify the origin of dielectric permittivity in plants, offering a conceptually grounded interpretation while keeping mathematical formalism to the level necessary for biological interpretation. We first outline the fundamental mechanisms of polarization, their characteristic time scales, and the frequency-dependent nature of the dielectric response, including the concept of complex permittivity, together with commonly used measurement approaches in biological materials. Particular attention is given to water, whose dielectric properties play a dominant role in plant tissues. We then examine how permittivity varies across different plant organs, including leaves, fruits, and roots, highlighting the relationship between dielectric response and structural and compositional features. Modeling strategies linking microscopic organization to macroscopic dielectric behavior are also discussed. Because dielectric permittivity is intrinsically connected to plant structure and composition, non-invasive measurements offer significant potential for assessing plant physiological status, including the detection of changes induced by abiotic and biotic stresses. By bridging engineering approaches with plant physiology, this review provides a unified framework to interpret dielectric measurements in plants and supports their application in plant science and phenotyping. Full article

Ultra-high-voltage direct-current (UHVDC) transmission systems impose stringent requirements on the reliability of insulation materials used in converter transformer bushings. Epoxy resin systems are key insulating materials in resin-impregnated paper (RIP) capacitor bushings, and their processing characteristics, curing behavior, and electrical properties directly affect bushing performance. In this study, two epoxy insulation systems used for resin-impregnated paper (RIP) bushings, namely the imported Araldite LY1564/Aradur 3486 system and the domestic EP-2020/CA-3015 system, were systematically investigated through viscosity, curing, and electrical property tests. The results show that the viscosities of both resins decreased significantly with increasing temperature. At 60 °C, the viscosities of Resin A and Resin B were 151.6 mPa·s and 156.3 mPa·s, respectively. The mixed resin–hardener systems exhibited similar viscosity evolution and comparable pot life characteristics. DSC measurements revealed two-stage curing reactions for both materials, with first exothermic peak temperatures of 65.4 °C and 96.3 °C and second peak temperatures of 269.3 °C and 269.8 °C for Materials A and B, respectively. Electrical testing demonstrated that both materials exhibited similar temperature-dependent dielectric and resistivity behavior, with dielectric loss increasing at elevated temperatures and resistivity decreasing as temperature increased. The volume resistivity trends and dielectric characteristics of the two materials remained highly consistent throughout the investigated temperature range. The results indicate that Material B exhibits processing performance, curing characteristics, and electrical insulation properties comparable to those of Material A. Therefore, Material B demonstrates strong potential for application in UHVDC RIP bushing insulation systems and provides a promising alternative for the localization of key insulating materials. Full article

Regenerated cellulose is a promising tribopositive material for sustainable triboelectric nanogenerators (TENGs), although its electrical output remains sensitive to surface and interfacial properties. In this study, regenerated cellulose was modified using atomic layer deposition (ALD) of Al₂O₃, TiO₂, and ZnO to investigate how nanoscale oxide coatings influence triboelectric performance against a tribonegative PTFE counter layer. Two deposition regimes were examined: 7 ALD cycles, representing the early stage of ALD growth, and 200 cycles, representing a more developed coating regime. Triboelectric measurements, dielectric spectroscopy, structural characterization and contact angle analysis, were used to evaluate how ALD modification influences the electrical response of regenerated cellulose. All ALD-modified samples exhibited increased surface charge density and power output compared to unmodified cellulose, while also showing improved retention of triboelectric performance at elevated relative humidity. The 7-cycle samples consistently outperformed the corresponding 200-cycle coatings under low-humidity conditions, whereas the 200-cycle ZnO sample exhibited the highest humidity stability. No direct correlation between wettability and triboelectric output was observed. The results suggest that relatively small interfacial modifications introduced by ALD are sufficient to influence both the triboelectric response and humidity-dependent charge dissipation behavior of regenerated cellulose. Full article

Reliable insulation design for LNG feedthroughs requires fundamental dielectric breakdown data obtained under cryogenic LNG conditions. However, such data remain scarce owing to the explosion-proof requirements imposed by the flammable nature of LNG. Furthermore, the influence of phase differences between LNG and NG on creepage dielectric breakdown behavior along insulation surfaces has received little attention. In this study, an explosion-proof cryostat and test facility compliant with the IEC 60079 series of standards were developed, and dielectric breakdown tests were conducted over a range of electrode gap distances and pressures. Two electrode configurations were employed: rod–plate electrodes for dielectric breakdown characterization in LN₂ and LNG, and creepage electrodes for surface dielectric breakdown evaluation in NG and LNG. Experimental results show that LNG requires approximately 1–2 bar of additional operating pressure above that of LN₂ to achieve equivalent dielectric strength. Moreover, LNG exhibited higher creepage dielectric breakdown voltages than NG under all test conditions, with the difference becoming more pronounced as pressure and creepage distance increased. Post-breakdown surface analysis revealed distinct differences in carbonization patterns between the two media. The findings of this study are expected to serve as fundamental reference data for the insulation design of LNG-based cryogenic feedthroughs. Full article

An Al₂O₃/AlN stack deposited via Atomic Layer Deposition (ALD) methods as a gate insulator for silicon carbide (4H-SiC) has been investigated, focusing on the effects of different Al₂O₃ deposition processes on the nitride layer. In particular, dielectric stacks, consisting of a 10 nm AlN interface (001)-oriented layer directly grown on a 4H–SiC substrate and in 20 nm of additional amorphous Al₂O₃ layers were synthesized in sequential deposition runs by thermal ALD (T-ALD) or plasma-enhanced ALD (PEALD) methods. The evolution of the phenomena occurring at the Al₂O₃/AlN interfaces has been established by in situ ellipsometry measurements. Strong effects of the oxygen plasma because of the O-Al-N bond formation have been clearly observed and corroborated by ex situ structural and electrical characterizations, especially in the case of the plasma-enhanced Al₂O₃ process. In particular, the Al₂O₃/AlN bilayer grown by the Al₂O₃ T-ALD method exhibited good insulating behavior and an 8.7-high dielectric constant was measured. By contrast, the Al₂O₃/AlN bilayer grown by the Al₂O₃ PEALD method demonstrated poor insulating properties. Full article

In this study, twin screw extruded Polyetherimide (PEI)/Poly(ethylene terephthalate) (PET) polymer blends (90/10, 70/30, 50/50 w/w%) were investigated to elucidate the composition–property relationship governed by morphological, structural, rheological, thermomechanical, mechanical, and electromagnetic shielding (EMI) performance behavior. Among other polymer blends, the 70/30 blend exhibits superior thermomechanical stability with a significant glass transition temperature of 132.7 °C, where a robust confinement effect effectively restricts the mobility of PET chains. This morphology, characterized by a domain size of 562 nm, provides proof of concept for interface-driven attenuation, reaching a maximum EMI shielding effectiveness of 2.54 dB within the investigated blends. This performance is primarily governed by Maxwell–Wagner–Sillars polarization at the immiscible boundaries, alongside an optimized dielectric loss of tan δ ≈ 0.065. The design of these high-temperature PEI blends provides a proof of concept for interface-driven attenuation and demonstrates their potential for developing advanced EMI shielding matrices. Full article

Chromic materials exhibiting reversible changes in optical properties under external stimuli represent an important class of smart materials with applications in smart windows, sensors, and optoelectronic devices. Transition-metal oxides (TMOs) provide a versatile platform for chromic functionality due to their coupled structural, electronic, and optical properties. In this review, the chromic response of selected TMO thin films is analyzed using both microscopic and phenomenological approaches. The microscopic description is based on many-body theory, including Green’s function methods and correlation effects, while the macroscopic optical response is described using Drude–Lorentz and Tauc–Lorentz models within the effective medium approximation. Chromic behavior in TMOs is shown to originate from two principal mechanisms: (i) electronic and structural reconstruction driven by Peierls–Mott metal–insulator phase transitions, leading to thermochromism (notably in VO₂ and V₂O₃), and (ii) formation of localized states driven by small-polaron injection, giving rise to electrochromism, gasochromism, and photochromism. The models are applied to representative systems, including VO₂, WO₃, NiO, and TiO₂, demonstrating the chromic changes in the dielectric function spectra. These results highlight chromism in TMOs as a multiscale phenomenon linking microscopic interactions with macroscopic optical response. Full article

Disk triboelectric nanogenerator (TENG) design pursues high structural figure of merit (${\mathrm{FOM}}_S$), yet nominal peak designs often sit in regions with steep geometric gradients; under a controlled $\pm 10\%$ symmetric perturbation proxy, worst-case ${\mathrm{FOM}}_S$ retention near the peak frontier falls to 2.7%. We decompose ${\mathrm{FOM}}_S$ into a charge-transfer channel ($Q_{\mathrm{sc},\mathrm{MACRS}}$) and a capacitance channel ($C_{\mathrm{sum}}^{-1}$), and train a multi-output surrogate with a physics consistency constraint on 1944 COMSOL simulations to jointly predict $Q_{\mathrm{sc},\mathrm{MACRS}}$, $C_{\mathrm{sum}}^{-1}$, and ${\mathrm{FOM}}_S$ across electrode-pair number, dielectric-thickness-to-radius ratio ($h/R$), air-gap-to-radius ratio ($d/R$), and dielectric constant. Evaluating 7776 design points reveals that 58.6% of the explored space is charge-dominant, 36.1% mixed, and 5.3% capacitance-dominant; raising dielectric constant shifts the mechanism toward capacitance-limited behavior, while a larger air gap reinforces charge-limited behavior. Mixed-regime windows tolerate the same perturbation proxy far better than peak-${\mathrm{FOM}}_S$ candidates, supplying candidate design windows for pre-fabrication screening within the validated simulation domain. The surrogate reaches pooled out-of-distribution ${\mathrm{FOM}}_S$$R_{{\log }_{10}}^2=0.914$ on 43 unseen structural and dielectric combinations. Delivered through an open-source Streamlit interface, the channel decomposition, mechanism mapping, and tolerance screening let designers identify the limiting mechanism and select candidate designs that are expected to tolerate geometric variation within the validated simulation domain, prior to fabrication. Full article

Lead sulfide quantum dots (PbS QDs), as a functional-layer coating, enable non-volatile integration and neuromorphic computing in memristive structures to address the von Neumann bottleneck. Herein, the dual-interface mechanism of PbS QDs in the memristor film structure is reviewed. First, the local electric field enhancement effect generates tip electrode-like structures in the coating film through QD-mediated spatial charge gradients, thereby enabling precise control over the nucleation and growth of conductive filaments (CFs). As a result, the consistency of switching voltages and the thermal stability at elevated temperatures are significantly improved. Conversely, the anion reservoir effect exploits surface dangling bonds on QDs to efficiently capture anions from the dielectric layer, thereby synergistically regulating vacancy migration kinetics. This process enables zero-initialization behavior and ultra-low-power operation. In addition, the spatial distribution design and density modulation of QDs further reinforce both mechanisms. The structural optimization of QD/dielectric interface engineering can simultaneously improve cycling endurance and resistive switching uniformity. Furthermore, modification of QD surface chemistry through ligand decoration and passivation suppresses the stochasticity of ionic diffusion while improving the linearity of synaptic weight updates. This interfacial engineering strategy utilizing QDs as coating films advances the development of high-performance photonic–electronic systems for memory–computing convergence. Full article

This paper presents a method for estimating moisture content (%MC) in power transformers. It primarily relies on the analysis of the statistical properties of relaxation times characterizing the dielectric frequency response (DFR), which is fitted as a sum of rational functions using the Vector Fitting (VF) tool. The DFR is modeled as a sum of Debye terms (accounting for materials exhibiting different relaxation times due to multiple polarization processes) characterized by poles and residues provided by VF. These parameters are then used to derive statistical factors that correlate with the shape of the dielectric response curve in the context of the Havriliak–Negami (HN) model, which is known for its effectiveness in characterizing materials with multiple relaxation times. By correlating the statistical factors with the HN model parameters, substantial insights into the insulation condition can be achieved. A moisture index (MI) is proposed from these parameters, which, when combined with conductivity, allows for accurate %MC estimation in the solid insulation system (cellulose). The combined MI and conductivity capture combined effects on moisture behavior, addressing both conductivity and polarization losses at different frequencies. The proposed method provides an efficient and straightforward non-invasive approach to insulation assessment without complex optimization algorithms. Experimental work on transformers at varying moisture levels provides validation of the proposed approach and demonstrates strong correlation with industry standards. The results confirm its reliability for moisture evaluation in transformer monitoring. Full article

This study investigates graphene oxide/carboxymethyl cellulose composite membranes containing 3 wt.% graphene oxide. The influence of the carboxymethyl cellulose content on the structural organization, mechanical properties, electrical resistivity, and humidity-dependent conductivity was systematically analyzed using Fourier transform infrared spectroscopy, scanning electron microscopy, X-ray diffraction, tensile testing, and electrical measurements. Fourier transform infrared spectroscopy indicated intermolecular interactions between graphene oxide and carboxymethyl cellulose functional groups. X-ray diffraction analysis showed gradual inter-layer expansion from 0.71 to 0.87 nm together with crystallite size reduction after polymer incorporation. Scanning electron microscopy observations demonstrated the increasing structural uniformity and polymer encapsulation of graphene oxide sheets with the increasing carboxymethyl cellulose content. Mechanical testing revealed improvement in the tensile strength from 6.6 to 17.8 MPa with the increasing carboxymethyl cellulose concentration. Simultaneously, the dry-state electrical resistivity increased from 5.8 × 10⁶ to 2.32 × 10⁷ Ω·m due to increasing dielectric separation between graphene oxide domains. Humidity-sensing experiments demonstrated reversible resistance changes in the 20–90% relative humidity range, associated with proton-assisted conduction through adsorbed water layers. The obtained results demonstrate that polymer incorporation strongly influences both the structural organization and electrophysical behavior of graphene oxide/carboxymethyl cellulose composite membranes. Full article

New lacunary Keggin-type polyoxometalate salts with the formula Cs₅PMMo₁₁(H₂O)O₃₉ (M = Cu, Zn) were synthesized via the inorganic solution condensation method. X-ray diffraction and FT-IR spectroscopy confirmed the preservation of the Keggin structure. The surface morphology and elemental composition were characterized using scanning electron microscopy coupled with energy-dispersive X-ray spectroscopy. Thermal analysis, performed by differential scanning calorimetry coupled with thermogravimetry, demonstrated a significant enhancement in thermal stability upon the incorporation of the transition metals into the heteropolyacid framework. Specifically, the substitution of protons by cesium and of molybdenum by copper or zinc positively influenced the crystallographic configuration of the salts, raising their thermal resistance (up to 526 °C). Furthermore, optical and dielectric measurements revealed promising electronic properties in the synthesized lacunary salts. Notably, the compound Cs₅PZnMo₁₁(H₂O)O₃₉ exhibited a substantially increased dielectric constant at low frequency, underscoring the synergistic effect of zinc addition on its dielectric performance. Full article

Flexible oxide electronics require dielectric layers that combine low-temperature processability, low leakage current, high capacitance density, and mechanical reliability. In this work, we prepared ZrAlO_x-PVP hybrid dielectric films through a low-temperature self-combustion solution process at 180 °C and systematically investigated the effect of PVP doping (0–2 wt%). The results show that PVP promotes the formation of M-O-C related bonding environments, suggesting the construction of an organic–inorganic crosslinked structure. Moderate PVP incorporation effectively suppresses leakage pathways, whereas excessive PVP induces polymer aggregation and trap-assisted conduction. Among all samples, the film on flexible PI (polyimide) with a PVP doping concentration of 0.5 wt% exhibits the best overall performance, with a leakage current as low as 1.89 × 10⁻⁸ A/cm² at 1 MV/cm, a dielectric constant of 8.88. After static bending at a radius of 20 mm, the film maintains stable dielectric behavior, indicating improved stress tolerance. Flexible IGZO TFT fabricated with the optimized dielectric shows a mobility of 11.84 cm² V⁻¹ s⁻¹, a threshold voltage of 0.48 V, and a subthreshold swing of 0.24 V dec⁻¹ before bending. This work demonstrates that moderate PVP crosslinking provides an effective balance between defect suppression and stress relaxation, offering a practical interface-engineering strategy for low-temperature flexible high-k dielectrics. Full article

Carbon/inorganic hybrid composites have evolved from filler-reinforced materials into design platforms for coupled electromagnetic, thermal, sensing, environmental, protective and energy-related functions. Their distinctive value lies in the possibility of combining a conductive, polarizable or porous carbon phase with an inorganic phase that contributes dielectric, magnetic, catalytic, ionic, thermally conductive or barrier behavior. This review examines carbon/inorganic hybrid multifunctional composites from the viewpoint of structure–property relationships, with emphasis on interfacial design, percolation, anisotropy, hierarchical architecture, processing and metrology. Selected graphitic composite studies are discussed as case studies for broadband dielectric spectroscopy, microwave shielding, high-frequency contact metrology, thermal diffusivity analysis and impedance-monitored graphene filters; these case studies are integrated with the broader international literature on CNT and graphene polymer composites, MXene films and foams, graphene/metal oxide photocatalysts, boron nitride/carbon thermal networks, biochar–graphene adsorbents, smart coatings, sensors, supercapacitors and water remediation systems. The central argument is that credible multifunctionality requires more than measuring several properties on the same material. It requires simultaneous or service-relevant co-optimization under constraints of thickness, density, processability, aging, humidity, corrosive media, regeneration, toxicity, economic feasibility and scalable fabrication. The review concludes with design rules and reporting recommendations intended to help move the field from impressive property demonstrations toward application-ready hybrid material systems. Full article

This study investigates the dielectric relaxation and conduction mechanisms in $S{e}_{90}S{n}_{6}P{b}_4$ chalcogenide glassy material, which is of interest for applications in phase-change memory devices, optical memory, and thermoelectric sensors. Despite previous studies on chalcogenide glasses, the conduction mechanisms at varying temperatures and the role of correlated barrier hopping (CBH) remain unclear. Using impedance spectroscopy in the frequency range 1 Hz–1 MHz at temperatures from 288 K to 318 K, the real ($Z\prime$) and imaginary ($Z″$) parts of the complex impedance were recorded. The sample was also characterized by X-ray diffraction (XRD) to confirm its glassy nature, and X-ray photoelectron spectroscopy (XPS) to determine the surface chemical composition and oxidation states of the elements. Peaks in $Z″$ at each temperature were used to evaluate the relaxation time τ, revealing thermally activated processes with an activation energy of 0.62 eV. Nyquist plots showed semicircular behavior with decreasing radii at higher temperatures, indicating enhanced d.c. conductivity with an activation energy of 0.63 eV. A.C. conductivity analysis demonstrated frequency-dependent behavior consistent with the CBH model, with hopping energy calculated as 0.32 eV. The dielectric loss increased with temperature and decreased with frequency, stabilizing above 250 Hz at 318 K. These findings provide new insights into the dielectric and conduction properties of $S{e}_{90}S{n}_{6}P{b}_4$ glasses, supporting their optimization for practical electronic applications. Full article